1. Field of the Invention
The present invention relates to pressure-contact semiconductor devices, in particular, explosion-proof structures of packages therefor.
2. Description of the Related Art
Pressure-contact semiconductor devices have been used in various fields of application systems such as inverters for industrial use and drive devices of fans and pumps. In these systems, an excessive short-circuit current (accident current) such as lightning-surge current may happen to flow, which needs an explosion-proof of a pressure-contact semiconductor device from system protection point of view.
In a conventional pressure-contact semiconductor device, a semiconductor chip (semiconductor substrate) is sandwiched between external electrodes (main electrode blocks) disposed on the top and bottom thereof, and tightly sealed by joining metal flanges attached to the external electrodes to the top and bottom of an external-surrounding insulator (insulating container). Two annular partition insulators (elastic members) are interposed, in parallel to each other inside the flanges in the surrounding insulator, across the outer peripheral surfaces of the external electrodes and the inner wall of the surrounding insulator, which prevents arcs, generated at the time of breakage of the semiconductor chip, from blowing out through weak portions such as the flanges to outside the package of the semiconductor device (refer to, for example, Japanese Patent Laid-Open No. 5-259302, FIG. 1 (Patent Document 1) and Japanese Patent Laid-Open No. 56-35439, FIG. 2 (Patent Document 2)).
In the conventional pressure-contact semiconductor device, since the annular partition insulators are interposed, in parallel to each other inside the flanges in the surrounding insulator, across the outer peripheral surfaces of the external electrodes and the inner wall of the surrounding insulator, the annular partition insulators are fitted onto the outer peripheral surfaces of the external electrodes and the inner wall of the surrounding insulator, to protect the flanges. In order to improve explosion-proof, a structure is required that makes no clearances at fitting portions between the partition insulator and the outer peripheral surfaces of the external electrodes or the inner wall of the surrounding insulator. Since radial centering is necessary in welding the flange, clearances are generally made between the external electrodes and the partition insulators in order to allow tolerance of these parts. For that reason, arcs generated from the semiconductor chip may sometimes reach through the clearances the outside of the device as breaking through the flanges. Therefore, sufficient explosion resistance has not been obtained.
On the other hand, in order to construct to eliminate the clearances, a machining process such as grinding or abrading needs to be implemented to improve dimensional accuracy of the surrounding insulator, the external electrodes, and the like. Moreover, even in a case of eliminating the clearances, works such as press-fitting of the elastic members are involved in the assembly processes. Consequently, its workability lowers and a substantial time is required to assemble them, which considerably increases its costs.